1. Technical Field
Embodiments of the present disclosure relate to voltage regulators and, more particularly, to a voltage regulator for filtering noise included in an input voltage and a power delivering device including the voltage regulator.
2. Discussion of Related Art
A voltage regulator is used to stably supply power to an electronic device. Voltage regulators are classified into linear regulators and switching regulators. A DC-DC converter is one type of switching regulator. The DC-DC converter has high converting efficiency. However, an output voltage of the DC-DC converter includes more noise than that of a linear regulator.
A low-dropout regulator (hereinafter referred to as “LDO regulator”) is one type of linear regulator. The LDO regulator has low converting efficiency, but has a fast response speed. An output voltage of the LDO regulator includes less noise than that of a DC-DC converter. Further, the LDO regulator may be used to supply power to a noise-sensitive device or a device that needs to be driven with high performance.
A power supply rejection ratio (hereinafter referred to as “PSRR”) is a ratio of output voltage noise to input voltage noise. The PSRR is used as an index to indicate the degree to which input voltage noise is effectively cut off in a specific frequency band by a voltage regulator to stably supply a voltage. When noise is included in an input voltage of the voltage regulator, an output voltage of the voltage regulator is not maintained at a constant value due to the noise. In particular, input voltage noise of a linear regulator is not effectively cut off in a high-frequency band between several hundreds of kilohertz (kHz) and several megahertz (MHz) that is greater than a gain crossover frequency of a closed circuit loop of a linear regulator. Therefore, it is difficult to generate a stable output voltage in a high-frequency band.